Ferritin, the major iron-storage protein of humans, exists in a variety of isomeric forms (isoferritins) in normal and cancer cells. The relationship between the altered structure of tumor isoferritins and the pathological variations in iron metabolism that are characteristic of organisms with cancer remains largely unknown. Our initial studies have shown that pure unfractionated ferritin from the relatively well-differentiated BH3 transplantable mouse hepatoma differs structurally from the ferritin in adult mouse liver. Nevertheless, both the normal and neoplastic ferritin populations appear to be derived from the same types of subunits. The functional capabilities of the hepatoma and liver ferritins now are being evaluated. Specific goals of the proposed continued research program will be the acquisition of new knowledge answering the following significant questions: (1) Are isoferritins within the tumor ferritin structurally different from those in the ferritin population of normal adult livers? (2) Do the hepatoma isoferritins have functional properties that differ from those of normal liver isoferritins? (3) Are these "tumor ferritins" specific or are they also found in other adult mouse tissues (e.g., heart or kidney), and, is any subunit unique to the neoplastic metalloproteins? (4) Which cells in the tumor contain ferritin? Analytical and preparative isoelectric focusing on polyacrylamide gels will be used to generate comparative isoferritin profiles, and to yield pure isoferritins for the assays of functional capabilities. Iron uptake, core formation, and iron release by specific isoferritins (as opposed to the whole populations being evaluated at present) will be conducted by means of correlated biochemical and ultrastructural assays. Subunit and polymer specificity will be analyzed by using acid-urea and standard polyacrylamide gel electrophoresis. Electron microscopy of thin sections will be used to determine the relative presence of ferritin in the different neoplastic and host cell types of these tumors.